71M6515H
Energy Meter IC
DATA SHEET
MARCH 2008
Registers Controlling Temperature Measurement and Compensation
DEG_SCALE (0x1C)
This register holds the scale factor used to calculate the internal temperature value provided by the temperature sensor to
temperature in degrees Celsius (°C). The default value is 22721 and should not be changed.
FREQ_DELTA_T (0x11)
This register holds frequency and temperature information in two bytes each.
31
16 15
DELTA_T
0
FREQUENCY (see Output Registers)
Bits 15-0: These bits (DELTA_T) represent the temperature information relative to the value stored in the TEMP_NOM
register. One LSB is equivalent to 0.1°C. The formula used for DELTA_T is:
DELTA_T = -DEGSCALE*2-22*(TEMP_RAW-TEMP_NOM)
TEMP_NOM (0x13)
This register holds the nominal (reference) temperature. During calibration, the host must write the value read from
TEMP_RAW to TEMP_NOM in order to enable temperature compensation. See the Meter Calibration section for details. The
temperature available in register DELTA_T is based on the difference between the current temperature, as provided in
TEMP_RAW, and the reference temperature provided by TEMP_NOM.
TEMP_RAW (0x12)
This read-only register holds the raw temperature provided by the temperature sensor on the 71M6515H chip. During
calibration, the host must write the value read from TEMP_RAW to TEMP_NOM in order to enable temperature
compensation.
Example: At calibration time, the raw temperature value of 853030 was read from the TEMP_RAW register and
written to the TEMP_NOM register. At a later time, the raw temperature register reads 844866. The 71M6515H
calculates the temperature difference to:
DELTA_T = -DEGSCALE*2-22*(TEMP_RAW-TEMP_NOM) = 44
This value is interpreted as +4.4°C.
PPMC1_2 (0x1B)
This register holds the linear and squared compensation factors for the ADC temperature compensation. The allowed
range is (215 – 1) to – (215 – 1). Both words are reset to zero if TEMP_NOM equals zero.
31
16 15
0
PPMC = ADC linear factor (PPMC = 26.84 * PPM/°C )
PPMC2 = ADC quadratic factor (PPMC2 = 1374 * PPM/°C2)
Changes to PPMC1_2 by the host are only allowed if the DEFAULT_PPM bit in the CONFIG register is zero. If additional
temperature compensation by the host, e.g. for external components, is required, the procedure is as follows:
1) The host sets the DEFAULT_PPM bit in the CONFIG register to 1 and then reads PPMC and PPMC2.
2) The host then adds the compensation factors to PPMC and PPMC2, resets the DEFAULT_PPM bit in the CONFIG
register to 0 and then writes the modified values to PPMC and PPMC2.
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